A study in adult rats of the peripheral modulatory influences on lateral preoptic, lateral hypothalamic (LH), and thalamic taste nucleus neurons and relevant neural transmitters involved in ingestive behavior. The results of additional neuropharmacological tests will be helpful in the possible development of anorectic agents with possible applications in the control of overeating, obesity, and the management of body weight. The specific purposes are (a) to establish the relations of peripheral sensory presynaptic (oral, gastrointestinal and hepatic) inputs associated with eating and drinking to lateral preoptic, LH and thalamic taste nucleus neurons; (b) to demonstrate the role of the vagus, splanchnic and glossopharyngeal nerves in the mediation of these effects; (c) to establish the involvement of ventral thalamic afferents and ventral tegmental efferents in these effects; (d) to determine by means of microiontophoresis and extracellular recording of action potentials in conjunction with neuropharmacological testing the role of noradrenaline, acetylcholine, serotonin, dopamine, and gamma-aminobutyric acid in the central mediation of these peripheral stimuli; and (e) to utilize horseradish peroxidase histochemical techniques to identify cell types sensitive to changes in blood composition and relevant peripheral stimulation. Also, relevant portions of the brain making presynaptic connections will be revealed by the retrograde transport of HRP. Statistical treatment of spike train data, including complete interval analysis, will be accomplished by means of a minicomputer.